A problem, in neuroscience, is how to deliver light in a complex, 3D pattern to different locations in a mammalian brain. A further problem is how to deliver light into different layers of neural tissue, in such a way that the light pulses are in a direction parallel to these layers.
Prior to this invention, neither could be done.
To understand why these problems are important, it is helpful to understand recent advances in phototherapy. Recently, optogenetic reagents have been used to facilitate optical control of neural circuits in mammalian brains. These reagents include channelrhodopsin-2 (ChR2), N. pharaonis halorhodopsin (Halo/NpHR), a variant of halorhodopsin, ss-Prl-Halo (sPHalo), an opsin (Arch) derived from an archaebacterium, and an opsin (Mac) derived from the fungus Leptosphaeria maculans. For example, a neuron that has been exposed to such a reagent may, upon exposure to a certain wavelength of light, be activated or silenced.
Many neural circuits in mammalian brains are 3-dimensional and geometrically complex. The ability to optically drive or silence neural activity in complexly-shaped brain circuits (such as the entire CA1 region of the hippocampus, the reticular nucleus of the thalamus, or a specific layer of frontal cortex), for milliseconds to seconds at a time, would be highly desirable.
A “lightguide” means an optical waveguide.
Prior to this invention, lightguides were able only to deliver light along a single pathway to a single location. They were not able to deliver light in 2D or 3D patterns to multiple locations, much less to deliver light to multiple layers of tissue in a direction parallel to these layers.
Some existing 2D arrays of light emitting diodes (LEDs) can produce light in 2D patterns. However, they suffer from a major disadvantage for neuroscience applications: the LEDs produce too much heat. When such an LED array is inserted into a mammalian brain, the heat from the LEDs interferes with neural function or its measurement, and may even harm neural tissue.